(1) Field of the Invention
This invention relates to methods and apparatus for two-dimensional radiation detection for use in converting X-ray images into electric signals in X-ray television systems used in medical diagnosis or non-destructive material testing, or converting, into electric signals, visible light resulting from optical reading of photographic subjects such as original documents.
(2) Description of the Related Art
In an X-ray television system which is one example of two-dimensional radiation detecting apparatus of the type noted above, an X-ray image intensifier and a television pickup tube are combined to convert X-ray images into electric signals. Specifically, X rays incident on the image intensifier are converted into visible rays by a converting film such as of CsI, and then electrons are released from a photoconductive surface. These electrons are accelerated and projected to an output fluorescent film to be converted into visible light, whereby the output fluorescent film outputs an image of visible light. The pickup tube is optically coupled to an output plane of the image intensifier. The image of visible light is projected through an optical lens or the like to an image pickup plane of the pickup tube, whereby electric charges corresponding to the incident light accumulate on the pickup plane. An electron beam scans and reads the electric charges, and outputs electric signals.
A two-dimensional CCD (Charge Coupled Device) camera is a well-known device for converting visible light images into electric signals.
However, to acquire final electric image signals from an X-ray image, the conventional X-ray television system having the combination of an X-ray image intensifier and a television pickup tube requires numerous steps of conversion from X rays to visible rays, then to electrons, to visible rays, through optics to visible rays, and to electric signals as noted above. Such a process tends to provide a poor efficiency of conversion, and inevitably causes a final image to have a low signal to noise (S/N) ratio. In addition, the combination of the image intensifier and image pickup tube has a drawback of complicating and enlarging the apparatus.
Although the two-dimensional CCD camera has the advantage of compactness, it is difficult to secure an enlarged area because of its construction. This results in the drawback of requiring, as indispensable elements, optics for reducing visible light images of photographic subjects.